Some Beatles scholars have commented on a key change during the middle 8, but I strongly disagree. I hear the whole song in a single tonality (B-flat mixolydian), and while I definitely hear a tonal shift at the middle 8, I hear this same shift in most middle 8s. After all, the whole point of the middle 8 is to contrast the verses (and/or chorus), and oftentimes the way that is achieved is through tonal contrasts (meaning using different chords than were used in the other sections). This notion is something I want to return to in the near future.